Effects of Increased Calcium, Magnesium, and Potassium Ion Concentrations on Survival Conditions, Growth Performance, and Physiological Parameters in Sea Urchin (Strongylocentrotus intermedius)

This study examined the effects of calcium, magnesium, and potassium ion concentrations on <i>Strongylocentrotus intermedius</i> through seven experimental rearing groups: two calcium ion levels (550 mg/L and 733 mg/L), two magnesium ion levels (1727 mg/L and 2302 mg/L), two potassium ion levels (533 mg/L and 710 mg/L), and a control. After 45 days of cultivation, 733 mg/L of calcium ions significantly reduced the <i>S. intermedius</i> survival rate, while 550 mg/L of calcium ions had no significant adverse effects on survival, growth (SGR), the feed conversion ratio (FCR), gonad colour, or immune enzyme activity, and it significantly increased the gonad index (GI). Meanwhile, 2302 mg/L of magnesium ions caused 100% mortality within 2 days, and 1727 mg/L of magnesium ions significantly reduced the survival rate and SGR while increasing the FCR. Additionally, 710 mg/L of potassium ions had no significant impact on the survival rate but significantly reduced SGR, the GI, and gonad colour while increasing the FCR, whereas 533 mg/L of potassium ions showed no significant adverse effects on survival, SGR, the FCR, gonad colour, digestive enzyme activity, or immune enzyme activity. The study results indicate that when formulating artificial seawater using source water with elevated calcium, magnesium, and potassium ion concentrations for <i>S. intermedius</i> aquaculture, calcium ions under 550 mg/L and potassium ions under 533 mg/L are biologically acceptable. However, magnesium ions require adjustment to a narrow optimal range to ensure survival and physiological performance.